i) Field of the Invention
The present invention relates to a cold box, and particularly to a cold box which is usually loaded on a truck and carried thereby, which cools a storing room while cooling a cold-heat accumulating agent before the truck starts to run, and which secures that the storing room is cooled by the cold-heat accumulating agent during running.
ii) Description of Related Art
Japanese Patent Laid-Open No. 62-210369 discloses a refrigerator provided with a cold-heat accumulating agent, which is disposed in the body of a heat insulating box, a cooler in the cold box and a freezing cooler for the cold-heat accumulating agent. This publication discloses a technique in that the operation of a compressor is generally controlled by a temperature controller so that the temperature in the cold box is kept at a set temperature, while the compressor is forced to be driven regardless of the opening and closing actions of the temperature controller only during the time taken for freezing the cold-heat accumulating agent.
In the above described prior art, the cooler (a first evaporator) for cooling the inside of the cold box and the cooler (a second evaporator) for freezing the cold-heat accumulating agent are connected in series in a freezing cycle. If the operation of the compressor is stopped, it causes to stop the cooling of the cold box by the first evaporator and of the cold-heat accumulating agent by the second evaporator. Therefore, the compressor must be operated during the time required for freezing the cold-heat accumulating agent. However, the interior of the cold box is uncontrollably cooled, until the cold-heat accumulating agent is frozen. There is thus a problem in that the cold-heat accumulating agent cannot be frozen, while the temperature in the cold box being kept at a temperature within the ice temperature zone, which must be strictly controlled with a narrow control temperature width, i.e, a small allowable temperature difference, for example, about .+-.0.5.degree. C., for the set temperature.
Japanese Patent Laid-Open No. 1-102269 discloses a cold-heat accumulation type of cold reserving box in which a cold-heat accumulating agent and a cooler are contained. The box disclosed in this publication comprises the body of a cold reserving box comprising a cold-heat accumulating room, in which the cooler containing the cold-heat accumulating agent, a defrosting heater and an air-sending fan are installed, and a cold reserving room for keeping transport commodities such as foods or the like cold, a heat insulating partition which divides the cold accumulating room from the cold reserving room and in which an air hole and a ventilation fan are disposed, and a refrigerator unit disposed on the outside the cold reserving box body near the cold reserving room thereof.
This publication does not disclose whether or not the cold-heat accumulating agent, stored in the cold-heat accumulating room can be discharged from the storing room. If the cold-heat accumulating agent can be discharged from the storing room, the cold reserving box is not designed so that the control temperature of the cold-heat accumulating room containing the cooler can be changed when cold-heat accumulating agents having different freezing temperatures are stored in the cold-heat accumulating room. When the cold-heat accumulating agent having a freezing temperature extremely higher than the control temperature (15.degree. C. or more higher) is stored, the cold-heat accumulating agent is excessively cooled, and the cooling room is also excessively cooled. This inhibits the attainment of a desired temperature and thus creates a danger of deteriorating the quality of the commodities stored in the cold reserving storehouse.
If the cold-heat accumulating agent cannot be discharged from the storing room, when an attempt is made to control the temperature in the cold reserving room to a plurality of temperature zones, the cold reserving room is excessively cooled or insufficiently cooled in some cases.